package main

import "fmt"

func main() {

	var doubleMap map[string]map[string]string = make(map[string]map[string]string)
	_, ok := doubleMap["aa"]["bb"]
	fmt.Printf("doubleMap[aa][bb] is exist: %v", ok) // doubleMap[aa][bb] is exist: false
	if ok {
		fmt.Printf("the value of double[aa][bb] = %v\n", doubleMap["aa"]["bb"]) // 不会panic
	} else {
		// doubleMap["aa"]["bb"] = "cc" // 会panic
	}

}
